1. Field of the Invention
The present invention relates to an exposure apparatus for forming a micropattern, such as that required in a quantum dot device and a sub-wavelength structured device, and also relates to a mask for use in the exposure apparatus.
2. Description of the Related Art
With the increasing capacity of semiconductor memories and the trend toward higher speeds and higher packing density of CPU processors, it is essential to realize a finer microstructure with photolithography. The limit in micromachining achievable with a photolithography apparatus is generally on the order of about the wavelength of light used.
For that reason, the wavelength of light used in the photolithography apparatus has been shortened. At present, a near ultraviolet laser is employed as a light source and micromachining on the order of 0.1 μm is realized.
Thus, photolithography capable of providing a finer microstructure has been developed. To carry out the micromachining on the order of not larger than 0.1 μm, however, problems arise that must be solved, e.g., using a laser of shorter wavelength and developing a lens in such a wavelength range.
Meanwhile, a micromachining apparatus has been proposed in which a scanning near-field optical microscope (abbreviated to “SNOM” hereinafter) is employed as means for enabling micromachining on the order of not larger than 0.1 μm to be performed with the use of light. In the proposed apparatus, local exposure beyond a limit imposed by the wavelength of light is carried out on a resist by using near-field light projecting from a micro-opening with a size of not larger than 100 nm, for example.
In any photolithography apparatuses using the SNOM, however, the micromachining is performed in a similar manner to drawing with a single stroke by employing one (or several) optical probe (probes). Hence, a problem arises in that throughput is not improved.
As one method for overcoming such a problem, a near-field mask exposure technique is proposed in which light illuminates a rear surface of a photomask prepared by forming a pattern of openings of not larger than 0.1 μm in a light shield film, and transferring a pattern of the photomask onto a resist by using near-field light projecting through the opening pattern (see U.S. Pat. No. 6,171,730). The invention disclosed in U.S. Pat. No. 6,171,730 is superior and provides a great contribution to the fields of photolithography and semiconductor production technology.
On the other hand, it has also been proposed to employ a mask pattern, which has dot openings 1001 arranged as shown in FIG. 10, when forming a dot pattern with exposure based on the near-field mask exposure mentioned above.
However, if the opening size is reduced to form a dot pattern of a smaller size, there arises a risk that the intensity of the near-field light generated from the opening is reduced and the time required for the exposure is prolonged, thus resulting in a reduced throughput of the micromachining apparatus.